Sodium cyanide process and briquets formed therefrom

ABSTRACT

Predensifying anhydrous sodium cyanide crystals and then compacting the resulting classified granules produces anhydrous sodium cyanide in briquet form that possesses unique characteristics. The briquets are essentially nonporous in structure with unit density approaching true crystal density and possess uniform internal hardness, remarkable durability and a high rate of solution. Using closed circuit hot air for conveying and drying, reduces sodium carbonate and formate content and the sodium cyanide is high in chemical purity.

United States Patent Inventors William Riley Jenks;

Olyn Wayne Shannon, both of Memphis,

Tenn.

Appl. No. 824,354

Filed Apr. 28, 1969 Patented Oct. 26, 1971 Assignee E. I. du Pont deNemours and Company Wilmington, Del.

Continuation-impart of application Ser. No. 734,767, June 5, 1968, nowabandoned.

SODIUM CYANIDE PROCESS AND BRIQUETS FORMED THEREFROM 13 Claims, 8Drawing Figs.

U.S. Cl 23/84, 264/109 Int. Cl C0lc 3/10, B29j l/OO Field of Search23/84;

[56] References Cited UNITED STATES PATENTS 1,923,570 8/1933 Gabel 23/84FOREIGN PATENTS 842,077 7/1960 Great Britain 23/84 PrimaryExaminer-0scar R. Vertiz Assistant Examiner-Hoke S. MillerAttorney-Robert W. Black ABSTRACT: Predensifying anhydrous sodiumcyanide crystals and then compacting the resulting classified granulesproduces anhydrous sodium cyanide in briquet form that possesses uniquecharacteristics. The briquets are essentially nonporous in structurewith unit density approaching true crystal density and possess uniforminternal hardness, remarkable durability and a high rate of solution.Using closed circuit hot air for conveying and drying, reduces sodiumcarbonate and formate content and the sodium cyanide is high in chemicalpuri- FORCE T BREAK POUNDS PATENTEDnm 2s l97i SHEET F 4 I500 F K k /A,/moo H n s00 K J-TJ/FORIING PRESSURE m m PSI son PSI A son PSI o L I00I20 I I I o 200 INVENTORS TEMPERATURE or FEED T0 BRIOUETTER-O mum mmJENKS own was summon ATTORNEY PATENTEDUDI 26 I9?! 3,615,176

SHEET 20F 4 FIG. 3 2000 LE; l500 O E 2/ 2 FEED COMPOSITION Lu a-soIIESII g; FINER THAN 50 mu 3 m 80% 8-50 MESH 20% FINER THAN 50 II-ESHFEED TEMPERATURE 0' I 0 I0 so s so To so 90 I00 FoRmc PR unE-nPsl FIG.4a 875 IMPROVED BRIOUET ERon PRE-COIIPACTED FEED a AJNTERNAL HARDNESS L.-L L-L.-..L o REAsuREo 0N TRANSVERSE cm PARALLEL To RoLL FAcE EXTERNALHARDNESS 00 INVENTORS NILLIAN RILEY JENIIS OLYN WAYNE SHANNON KM/KMATTORNEY PATENTEDUBT 2s l97l 3.615.176

SHEET 30 4 FIG. 4b

- BRIOUET MADE Rumour PRs-comcnon or FEED :10

w INTERNAL DNESS g MEASURED TRANSVERSE cur 0-* PARALLEL T0 ROLL FACE. 2EXTERNAL HARDNESS.

o 20 so so I00. TRAVERSE DISTANCE.

FIG. 5 [PRE-DENSIFIED GRANULAR] L FEEDSTO0K@ noc l.590

L580 Emo /x :L560 5:.550

0 5 l0 I5 20 25 so FORMING RREssuRE-RPsI INVENTORS WI AN RILEY JEN 0LWAYNE SHAH BY MW ATTORNEY SODIUM CYANIDE PROCESS AND BRIQUE'IS FORMED'I'HEREFROM CROSS-REFERENCE TO RELATED APPLICATIONS This application isa continuation-in-part of copending ap- 5 BACKGROUND OF INVENTION 1.Field of Invention This invention relates to a sodium cyanide compactingprocess and anhydrous briquettes formed from the compacted sodiumcyanide.

2. Prior Art The production of sodium cyanide by the evaporation ofaqueous solutions of the same is well known. However, the dried productthus obtained is a fine, crystalline material which is difiicult tohandle due to the irritant and toxic nature of the dust associated withsuch handling. Various agglomeration techniques are employed in theindustry to offset this defect, such as tabletting, pelletizing orbriquetting the crystalline material. These compacted forms as hithertoproduced are, however, subject to degradation and breakage for onereason or another in the course of commercial handling and, thus,regenerate the dusting problem. The reasons vary but are generallyassociated with nonuniform internal softness, low density and weak bondsbetween the individual particles.

SUMMARY OF INVENTION According to the present invention there isprovided the process comprising: compacting sodium cyanide crystalshaving a moisture content of no more than 0.05 percent by weight underheat and pressure into a translucent, noncrystalline sheet or ribbon ofsodium cyanide; breaking the sodium cyanide sheet or ribbon intogranules having a maximum size of USS No. 4 (US. Sieve Series-A.S.T.M.E-ll-6l) with no more than l-25 percent of the granules finer than USSNo. 50; classifying the granules as required so that the granularproduct has no more than 1) percent of USS No. 50 fines and recyclingthe remaining fines from the classifier to the compactor.

There is also provided a sodium cyanide briquette comprising an internalportion of granules having a planar surface between granules exhibitinga bond essentially as strong as the cleavage strength of a sodiumcyanide crystal and an essentially uniform-type D Shore hardness of atleast 65 throughout and an external compacted portion of higherhardness, said briquette having a relative density of at least about0.97 and a solution rate equivalent of about 8-11 minutes standardsolution time.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic flow diagram of theprocess of the present invention;

FIG. 2 is a graph showing briquette durability as a function of granularfeed temperature at various pressures;

FIG. 3 is a graph showing briquette durability as a function of formingpressure at a granular feed temperature of 170C.;

FIG. 4a and 4b are graphs showing briquette uniformity as a function ofgranular feed character;

FIG. 5 is a graph showing the specific gravity of briquettes as afunction of forming pressures at a granular feed temperature of 170C.;

FIG. 6 is a graph showing the relation of briquette density to crystaldensity as a function of forming pressure at a granular feed temperatureof 170 C; and,

FIG. 7 is a graph showing briquette solution time as a function offorming pressure at a granular feed temperature of 1 70 C.

DETAILED DESCRIPTION OF INVENTION With reference to FIG. 1, crystallinesodium cyanide, produced by evaporative concentration of an aqueoussolution prepared by chemical reaction between hydrogen cyanide andaqueous caustic soda, is separated from the mother liquor by filtrationon rotary drum dryer-filter 10. Hot air is supplied to the filter hoodby the demister blower 11 through the air heater l5 and line 12 in thetemperature range of 250 to 450 C., preferably 375 to 400 C. The hot airaccomplishes some predrying of the filter cake and minimizes dryingrequirements further along in the process. The predrying reducesmoisture content sufficiently (below 5 percent by weight) so thatcontinuous feed without sticking and caking can be maintained to the airdryer venturi l4.

Partially dried sodium cyanide passes through mixing conveyor 13 whichsubdivides the partially dried cake so that no fragments in excess of 2inches maximum dimension remain, and a uniform feed can be maintained tothe dryer venturi l4. Essentially carbon dioxide free hot air is heatedin heater l5 and is introduced into dryer feed venturi 14 through line16 at a temperature within the range of 275 to 400 C., preferably 350 to375 C. The moist sodium cyanide crystals containing 2-5 percent water,but generally about 3 percent water, are pneumatically conveyed anddried adiabatically in line 17 to an essentially bone-dry state, i.e., amoisture content of less than about 0.05 percent, preferably 0.03percent by weight. The temperature and proportion of hot air to solidsfed to venturi 14 is adjusted so that the dried product discharged fromdryer-conveyor 17 is at a temperature within the range of to 250 C.,preferably 180 to 225 C. The dried product is discharged into cyclone 18to deposit the solids in compactor feed bin 19 while the drying air ispassed to blower 20 through line 21.

The dried sodium cyanide fines are compacted under heat and pressure inroll press 22 into a translucent, noncrystalline sheet or ribbon havinga density within the range of 1.550 to 1.590 and a preferred thicknessof about is to 3/ l6 inch. Compaction of the fines can be carried outover a wide temperature and pressure range. For example, the temperaturecan be within the range of 125 to 225 C. and the compression pressurecan be within the range of 5,000 to 15,000 p.s.i. although the preferredconditions are a temperature of 180 to 225 C. and a pressure of 6,000 to10,000 p.s.i. Under these conditions, the fines are converted to acontinuous semiplastic (bends) sheet or ribbon of uniform texture, withno evidence of crystallinity and possessing the translucency of milkyquartz and a density of 1.550 to 1,590. Ribbon thickness much abovethree-sixteenths inch, say one-fourth inch or thicker, is generallycharacterized by nonuniformity of compaction, perhaps due to difficultyin maintaining continuous uniform feed. This difficulty is compounded bythe natural bridging action of the solids as they are packed moreclosely and compressive forces tend to be dispersed and distorted. This,coupled with the fact that a thicker ribbon has to be cut more times tobe reduced to a USS No. 4 dimension, leads to excessive generation offines in the grinding step.

The semiplastic compacted sheet or ribbon is then fed to a prebreaker 23where it is partially broken into irregular chips of l to 2 inches insize and then to granulator 24, which is a modified hammer mill typeespecially adapted for controlled size reduction. By having the sodiumcyanide crystals compacted into sheet form, with properties as describedabove, size reduction is accomplished in prebreaker 23 and granulator 24without producing gross quantities of undesired fines. With selection ofthe proper type and number of hammers, rotor speeds, and internal sizingscreen, the granulator 24 produces a raw grind having no more than 10-25percent of the material finer than USS No. 50, the remainder beinggranules in the range of USS No. 4 to +USS No. 50. While hammers can beof various types, and can operate at top speeds of 50 to 100 feet persecond, preferred conditions for achieving the desired grind employ thehammers operating at tip speeds of 60 to 75 feet per second. Similarly,while sizing screens can be of various types, the preferred conditionsemploy screens with a minimum of 60 percent open area, with openings setto pass the largest particle size desired. However, if ribbontemperature is too low, or it the ribbon has been formed at too low acompaction pressure, the amount of fines generated during granulationwill increase rapidly, readily exceeding 50 percent of the raw grind.

The granulated sodium cyanide product is fed into the throat ofclassifier feed venturi 25 where it is pneumatically conveyed toclassifier 26 by line 27. Air to convey the granulated, predensifiedproduct is supplied to venturi 25 from blower 20 through line 28 and isthe same essentially carbon dioxide free air used to convey the moistcrystals to the compactor.

The granulated product is classified in classifier 26 in a hot airsystem so that the product from the classifier contains no more than 2)percent by weight of USS No. 50 fines and preferably l-l5 percent ofsuch material (This means there is a maximum of 15 percent finer thanUSS No. 50) and is at an elevated temperature. Part of the granulated,dense product is diverted through line 29 to granular product pack bin30. The rest of the granulated, predensified product passes through line31 to briquetter feed bin 32 and then to the rotary briquetting press33.

To accomplish the desired combination of properties, namely uniformdensity, durability and controlled solution rate of the briquettedproduct, the temperature of the predensified, classified granularproduct is within the range of 125 to 200 C. and the granular product isbriquetted at a pressure within the range of 5,000 to 45,000 p.s.i.However, in order to obtain the unique and preferred product qualifies,the predensified granular feed stock is briquetted at a temperaturewithin the range of 150 to 175 C. and a pressure within the range ofabout 8,000 to 15,000 p.s.i. preferably about 10,000 to 13,000 p.s.i.Under these latter conditions, a tough, durable briquette is obtainedwhich is characterized by a high relative density, unifonn internalhardness and a high rate of solution. Fracture and crystallographicstudies of the internal granular structure indicate that there is aplanar surface between granules and the bond between individual granuleshas become essentially as strong as the cleavage strength of the sodiumcyanide crystals themselves. A durable briquette is produced which canbe handled in drums, conveyors, etc., etc. without breakage and withoutdusting.

After briquetting, the briquettes are passes to rotary screen 34, wherethe fins," or thin layers of material attached to the periphery of thebriquette centerline, are removed and then to briquette pack bin 35.

The fines separated in classified 26, i.e., the material under USSSO-mesh, are recycled to the compactor feed bin 19 through line 36 byblower 37. The fines are deposited in bin 19 by cyclone 38 and the exitair in line 39 is fed blower 40 to a recycle scrubber and condenser 41through line 42 where the air is cooled to 50 to 60 C. and any hydrogencyanide and fine sodium cyanide dust that may be present are removed.The air then passes to another scrubber 43 through line 44 where waterremoved in the drying step and any remaining cyanides are removed. Hotair used to predry the filter cake on filter is also cooled and scrubbedin tower 43 to remove entrained liquor, and it joins line 44 throughline 45.

The air returns to blower 11 through line 46 and then to heater throughline 47 and, thus, recycles through the process. Totally enclosing andrecirculating the air eliminates exposure of the sodium cyanide tocarbon dioxide. This closed air loop coupled with adiabatic drying leadsto a substantial reduction in the sodium carbonate and sodium formatecontent of the product, and a minimum sodium cyanide assay of 99 percentis achieved.

The unique physical properties of the sodium cyanide briquettes are moreaccurately illustrated in FIGS. 2 to 7. Sodium cyanide crystals having amoisture content of under 0.03 percent by weight were predensified at180 to 190 C.

and a compaction pressure of 7,000 to 8,000 p.s.i. in a horizontal rollpress. The granular briquetting feed had a size range of 88 percent USSNo. 4 to +USS No. 50 and 12 per- I cent finer than USS No. 50. Thesegranules, having a particulate density of at least 1.55, were thenformed into briquettes at various temperatures and pressures.

The briquettes were then subjected to the following tests:

SOLUTION RATE The solution rate of the cyanide ovaloid briquettes inwater is determined by placing approximately 8 ounces of approximately0.5 ounce briquettes (to the nearest whole briquette) in a 6 inch high X4.5 inch diameter stainless steel wire basket 3 inch off the bottom of afour-liter beaker containing 1 gallon of water. The basket isconstructed of 30-mesh type 316 stainless steel screen with a wirediameter of 0.013 inch. The water temperature for the test is held at 60C., and care is taken so that no agitation is present. The time requiredfor the last trace of each briquette to disappear is recordedseparately. The average of these times for all briquettes is recordedunder the heading Solution Rate.

Crush Strength The briquette to be tested is placed on its side on thebottom platen of a Carver laboratory press. A l-inch diameter steelcylinder is then placed between the upper platen and the top side of thebriquette. The hydraulic pressure is then slowly increased. The gagepressure is recorded for (1) the appearance of the first visible crackwhich develops along the large transverse radian of the upper face ofthe briquette, and for (2) the point where the briquette and collapses.The crush strength is recorded as the pressure at which the firstvisible crack appears. Hardness Hardness tests are carried out at roomtemperature in a low relative humidity atmosphere (under 35 percent R.H.). To measure internal hardness, the briquettes are cut in half alongthe major axis in the plane perpendicular to the plane connecting theleading and trailing edges. The exposed cut surface are sanded smoothwith an extra-fine grit sandpaper. External hardness is measured on thesurface of the whole briquette along the intended line of cut. Thisouter case of higher hardness is observed to be about one-tenth inch inthickness, although it does vary from point to point over the briquette,and will vary somewhat with varying briquetting pressures. A ShoreDurometer, ASTM Designation D2240, type D, is applied to selectedreference points along the centerline to determine hardness." Sufficientpressure is applied to assure firm contact between the reference plateof the Durometer and the surface being measured. Dial readings (0-100)are taken within one second after firm contact is made, and are recordeddirectly as a measure of relative hardness. Specific Gravity To minimizerandom error, sample size for this test is taken as ten briquettes,selected as typical of the forming conditions imposed. The weight of thel0-briquette sample, in grams, is determined accurately to the firstdecimal place, i.e., to the nearest five hundredths gram. The briquettesare transferred to a calibrated container and a known volume of drywhite kerosene or other nonsolvent is added. The combined volume ofbriquettes-plus-liquid is then read to the nearest one-tenth milliliter,and the briquette volume obtained by difference. Briquette specificgravity is then calculated as follows:

weight of briquets Speclfic volume of briquets 1.596. At a relativedensity of 1.00, compacted density would be the same as true crystaldensity.

The results of the above-mentioned tests are shown in FIGS. 2 to 7. FIG.2 shows the effect of temperature of the feed and forming pressure onsodium cyanide briquette durability in terms of compressive forcerequired to break or crush the briquette. While the general trend wasanticipated, the apparent convergence of the 30,000 p.s.i. and the60,000 force lines at higher temperatures was unexpected.

The results of further investigation are shown in FIG. 3. This figureclearly shows the performance peak suggested in FIG. 2. The decline indurability at pressures above 45,000 p.s.i. is indicated by fracturestudies to be the result of generation of internal stress planes whichact as points of incipient cleavage. This is supported by the resultsshown in FIGS. 5 and 6, which show that compacted unit densities of1.594 are obtained at 30,000 p.s.i. forming pressures at a feedtemperature of 170 C., compared to the specific crystal density of1.596. This corresponds to a relative density of 0.998 as shown on FIG.6. At pressures higher than 45,000 p.s.i., and with having reached therelative density of 1.00, the excess pressure is expended in frictionallosses and the generation of internal stresses. A relative density of atleast 0.97 is a critical value based on a careful determination ofbriquette density. This corresponds to a briquette specific gravity ofabout 1.55. At a relative density of about (Sp. gr. of 1.53) thebriquettes are substantially less durable, and even though they have afaster solution rate, they are much less satisfactory for handling dueto attendant breakage and dusting.

Briquettes made at pressures up to 45,000 p.s.i., from precompacted orpredensified feedstocks exhibit a marked increase in internal uniformityas shown by the comparison of the graphs in FIGS. 40 and 4b.

Since rate of solution of briquetted sodium cyanide is of importance inmany end uses, the effect of forming pressures at 170 C. on thisproperty is shown in FIG. 7. This figure indicates that to obtain asolution rate of 8-1 1 minutes, a forming pressure of about 8,000 to15,000 is used. A solution rate of 9-10 minutes is preferred with acorresponding forming pressure ofabout 10,000 to 13,000 p.s.i.

The briquettes produced under the preferred conditions set forth hereinpossess a smooth, continuous surface of marked uniformity and with noporosity visible even under 4X to 8X magnification. Density of suchbriquettes can be determined directly, as described above, withoutfurther preparation. Briquettes produced under conditions outside thosedisclosed, as for example at lower forming pressure and/or at lowerfeedstock temperatures, will frequently possess porosity apparent evento the unaided eye. Such briquettes must be sealed with a thin coatingor film of clear lacquer or other impervious material and allowed to drycompletely before the specific density test is carried out. If not sotreated, liquid will penetrate into the briquette and the determinationswill be er roneous.

It should be recognized that potassium cyanide granules and briquettescan also be manufactured by the process of the present invention.Although commercially less important than sodium cyanide, the potassiumcyanide market requirements can be satisfied by occasionally running theprocess with potassium cyanide crystals.

We claim:

1. A process comprising: compacting sodium cyanide crystals having amoisture content of no more than 0.05 percent by weight under a pressurewithin the range of 5,000 to 15,000 p.s.i. and a temperature within therange of 125 to 225 C. into a translucent, noncrystalline sheet ofribbon of sodium cyanide; breaking the sodium cyanide sheet or ribboninto granules having a maximum size of USS No. 4 and having no more than10-25 percent of the granules finer than USS No. 50; classifying thegranules as required so that the granular product has no more thanpercent of USS No. 50 fines and recycling the remaining fines from theclassifying step to the compacting step 2. The process of claim 1wherein the compacting pressure is within the range of 6,000 to 10,000p.s.i. and the compacting temperature is within the range of 180to 225C.

3. The process of claim 1 wherein the compacted sheet has a densitywithin the range of 1.550 to 1.590.

4. The process of claim 1 wherein the compacted sheet has a thicknessbetween about one-eighth t0 three-sixteenths inch.

5. The process of claim 1 wherein the classified granules are formedinto briquettes at a pressure within the range of 5,000 to 45,000 p.s.i.and a temperature within the range of to 200C.

6. The process of claim 1 wherein the classified granules are formedinto briquettes at a pressure within the range of 8,000 to 15,000 p.s.i.and a temperature within the range of to C.

7. A process comprising: compacting sodium cyanide crystals having amoisture content of no more than 0.03 percent by weight at a pressurewithin the range of 5,000 to 15,000 p.s.i. and a temperature within therange of 125 to 225 C. into a translucent, noncrystalline sheet orribbon of sodium cyanide having density within the range of 1.550 to1.590; breaking the sodium cyanide sheet or ribbon into granules havinga maximum size of USS No. 4 and having no more than 10-25 percent of thegranules finer than USS No. 50; classifying the granules as required sothat the granular product has no more than 15 percent of USS No. 50fines; recycling the remaining fines from the classifying step to thecompacting step and forming the granules into briquettes at a pressurewithin the range of 8,000 to 15,000 p.s.i. and a tem perature within therange of 150 to 175C.

8. A process of preparing sodium cyanide briquettes from a solution ofsodium cyanide containing crystalline sodium cyanide comprising:filtering crystalline sodium cyanide; subdividing and pneumaticallyconveying and simultaneously drying adiabatically the filteredcrystalline sodium cyanide in an essentially carbon dioxide free hotairstream to a moisture content of not more than 0.05 percent by weight;compacting the dried sodium cyanide crystals into a translucent,noncrystalline sheet or ribbon of sodium cyanide; breaking the sheet orribbon into granules having a density within the range of 1.550 to 1.590and having a maximum size of USS No. 4 and having no more than 10-25percent of the granules finer than USS No. 50; pneumatically conveyingand classifying the granules as required to a granular product having nomore than 20 percent of USS No. 50 fines; recycling the remaining finesto the compacting step and forming the high-density granules intobriquettes at a pressure within the range of 5,000 to 45,000 p.s.i. anda temperature within the range of 125 to 200C.

9. The process of claim 8 wherein the filtered sodium cyanide ispredried with essentially carbon dioxide free air having a temperaturewithin the range of 250 to 450 C.

10. The process of claim 9 wherein the temperature of the conveying anddrying hot airstream is within the range of 275 to 400 C.

11. A sodium cyanide briquette consisting essentially of an internalportion of granules having a planar surface between granules exhibitinga bond essentially as strong as the cleavage strength of a sodiumcyanide crystal and an essentially uniform type D Shore hardness of atleast 65 throughout and an external compacted portion of higherhardness, said briquette having a relative density of at least about0.97 and a solution rate equivalent of about 8-1 1 minutes standardsolution time as determined by placing approximately 8 ounces ofapproximately 0.5 ounce briquettes in a 30-mesh stainless steel wirebasket 6 inches high by 4.5 inches in diameter and having a wirediameter of 0.013 inch, placing the basket 3 inches off the bottom of afour-liter beaker containing 1 gallon of nonagitated water at atemperature of 60C. and measuring the average time required for the lasttrace of each briquette to disappear.

2. The process of claim 1 wherein the compacting pressure is within therange of 6,000 to 10,000 p.s.i. and the compacting temperature is withinthe range of 180* to 225* C.
 3. The process of claim 1 wherein thecompacted sheet has a density within the range of 1.550 to 1.590.
 4. theprocess of claim 1 wherein the compacted sheet has a thickness betweenabout one-eighth t0 three-sixteenths inch.
 5. the process of claim 1wherein the classified granules are formed into briquettes at a pressurewithin the range of 5,000 to 45,000 p.s.i. and a temperature within therange of 125* to 200* C.
 6. The process of claim 1 wherein theclassified granules are formed into briquettes at a pressure within therange of 8,000 to 15,000 p.s.i. and a temperature within the range of150*to 175 =* C.
 7. A process comprising: compacting sodium cyanidecrystals having a moisture content of no more than 0.03 percent byweight at a pressure within the range of 5,000 to 15,000 p.s.i. and atemperature within the range of 125* to 225* C. into a translucent,noncrystalline sheet or ribbon of sodium cyanide having density withinthe range of 1.550 to 1.590; breaking the sodium cyanide sheet or ribboninto granules having a maximum size of USS No. 4 and having no more than10-25 percent of the granules finer than USS No. 50; classifying thegranules as required so that the granular product has no more than 15percent of USS No. 50 fines; recycling the remaining fines from theclassifying step to the compacting step and forming the granules intobriquettes at a pressure within the range of 8,000 to 15,000 p.s.i. anda temperature within the range of 150* to 175* C.
 8. A process ofpreparing sodium cyanide briquettes from a solution of sodium Cyanidecontaining crystalline sodium cyanide comprising: filtering crystallinesodium cyanide; subdividing and pneumatically conveying andsimultaneously drying adiabatically the filtered crystalline sodiumcyanide in an essentially carbon dioxide free hot airstream to amoisture content of not more than 0.05 percent by weight; compacting thedried sodium cyanide crystals into a translucent, noncrystalline sheetor ribbon of sodium cyanide; breaking the sheet or ribbon into granuleshaving a density within the range of 1.550 to 1.590 and having a maximumsize of USS No. 4 and having no more than 10-25 percent of the granulesfiner than USS No. 50; pneumatically conveying and classifying thegranules as required to a granular product having no more than 20percent of uss no. 50 fines; recycling the remaining fines to thecompacting step and forming the high-density granules into briquettes ata pressure within the range of 5,000 to 45,000 p.s.i. and a temperaturewithin the range of 125* to 200* C.
 9. The process of claim 8 whereinthe filtered sodium cyanide is predried with essentially carbon dioxidefree air having a temperature within the range of 250* to 450* C. 10.The process of claim 9 wherein the temperature of the conveying anddrying hot airstream is within the range of 275* to 400* C.
 11. A sodiumcyanide briquette consisting essentially of an internal portion ofgranules having a planar surface between granules exhibiting a bondessentially as strong as the cleavage strength of a sodium cyanidecrystal and an essentially uniform type D Shore hardness of at least 65throughout and an external compacted portion of higher hardness, saidbriquette having a relative density of at least about 0.97 and asolution rate equivalent of about 8-11 minutes standard solution time asdetermined by placing approximately 8 ounces of approximately 0.5 ouncebriquettes in a 30-mesh stainless steel wire basket 6 inches high by 4.5inches in diameter and having a wire diameter of 0.013 inch, placing thebasket 3 inches off the bottom of a four-liter beaker containing 1gallon of nonagitated water at a temperature of 60* C. and measuring theaverage time required for the last trace of each briquette to disappear.12. The sodium cyanide briquette of claim 11 wherein the externalcompacted portion is about one-tenth inch in thickness and has a type DShore hardness of about
 70. 13. The sodium cyanide briquette of claim 12wherein the solution rate equivalent is about 9-10 minutes standardsolution time.